It is desirable to determine the weight of a vehicle occupant of a vehicle seat. Upon the occurrence of a crash event, for example, an occupant restraint device may utilize an individual's weight to determine an appropriate amount of restraining force. One common type of weight sensor which may be mounted to a vehicle seat is a strain gauge sensor. Various other types of weight sensing devices have been proposed.
U.S. Pat. No. 2,968,031 to Higa discloses an electronic micrometer which measures rotational displacement by monitoring a tuned resonant circuit. The displacement of a movable member is detected by detuning the resonant circuit with a three element capacitive pick-off. An output voltage has a magnitude which is a function of both the magnitude of the input signal and the amount of displacement. In order to obtain accurate results, this circuit requires balancing the resonant circuit to the zero condition prior to each measurement.
U.S. Pat. No. 5,804,885 to Cadwell discloses a displacement measuring device which includes a variable capacitor. The variable capacitor provides a DC output signal having an amplitude which is proportional to displacement. The output signal is fed back to the variable capacitor to automatically re-balance the electrodes which form the capacitor. The feedback provides a measure of the force being transduced.
U.S. Pat. No. 4,384,496 to Gladwin similarly discloses a variable capacitor for measuring a load applied to a housing. The variable capacitor is connected within the housing and provides an output signal having an amplitude which varies according to the movement of the housing.